Exodus 12:23
When the Lord goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the doorframe and will pass over that doorway, and he will not permit the destroyer to enter your houses and strike you down. The mechanism of Passover protection is disclosed here: God sees the blood, and He will not permit the destroyer to enter. The destroyer — mashkhit, the destroying angel — operates under divine governance. Hebrews 11:28 says Moses observed the Passover so that the destroyer of the firstborn would not touch the firstborn of Israel. Revelation 9:4 describes the locust-like creatures being told not to harm those who have the seal of God on their foreheads — the Passover blood-on-the-door is the seal of God, the mark that identifies those who belong to Him and must not be touched. The protection is not self-generated; it is divinely granted and divinely enforced.